A straight line joining two opposite corners of a square, rectangle, or other straight-sided shape. The diagonal of the square divides it into two equal triangles.
A slanting line or direction; a line or direction that is not vertical or horizontal. The artist used a diagonal to create a sense of movement in the painting.
A line or cut across a fabric or material that is not parallel to the edges, often used in tailoring. The dress was cut on the diagonal to give it a more flattering fit.
In chess, a sequence of squares of the same colour that meet corner to corner, along which a bishop moves. The bishop controlled the long diagonal from a2 to g8.
The set of entries of a square matrix that lie from the top-left to the bottom-right corner (the main diagonal). The diagonal of the identity matrix consists of ones.